1. Field of the Invention
The present invention relates to purified water supply systems of the type having a reverse osmosis unit for producing purified water from an incoming supply of ordinary tap water or the like. The invention has particular application to water purifying systems of the type which do not require any electrical power.
2. Description of the Prior Art
Water purification by means of a reverse osmosis membrane has become well recognized in the art. Prior art water purifying systems have typically included a reverse osmosis unit which has an inlet coupled to a source of ordinary tap water or the like, and a purified water outlet coupled to a purified water storage tank and/or to a faucet or other remote usage location, and to a waste water drain. The reverse osmosis unit typically includes flow passages and valve means for controlling the flow of water through the system. In operation, tap water flows into the reverse osmosis unit and that portion which flows through the membrane is purified and passes to the storage tank and/or faucet, while waste water which does not pass through the membrane exits to the drain. A pre-filter unit may be used upstream of the reverse osmosis unit for removing particulates, and a post-filter unit, such as an activated charcoal filter, may be utilized between the reverse osmosis unit and the remote faucet or other usage location.
Prior art systems occasionally provide a shut-off valve which automatically closes the tap water inlet when the storage tank is filled with purified water, thereby to avoid wastage of tap water. However, it has been found that when the shutoff valve remains closed for an extended period of time, bacterial growth can occur in the system. Since such bacterial growth can be eliminated by continuous water flow, some prior art systems eliminate the shutoff valve to allow tap water to flow continuously through the system, thereby continuously washing the reverse osmosis membrane. However, in the typical system several gallons of tap water may flow to the drain for every gallon of purified water produced and, therefore, a continuous flow system results in substantial water wastage.
It is also known to provide a fixed flow to the drain, but prior art systems have not permitted variation of the rate of flow to the drain. Furthermore, contaminants in the drain water may build up on the inlet side of the drain and can eventually clog the drain.